Please help me with this question:
One of the cardinal features of the immune system is its ability to
discriminate self from nonself. Recent experimental evidence suggests
that a two signal model of lymphocyte activation is the biological basis
for S/NS discrimination. For CD4+ T cells, signal two is delivered by
the antigen presenting cell.
Here is the question:
Since antigen presenting cells take in antigens randomly from their
environment, how is their delivery of signal two regulated so as to
achieve a self/nonself discrimination?